Quaternary variability of Indian Ocean monsoon winds and climate.

摘要

Satellite and meteorological observations, aerosol measurements, sediment trap studies, and studies of the mineralogical distribution of surface sediments, indicate an eolian transport mechanism for the lithogenic component of modern Arabian Sea sediments. Sediment cores from the Owen Ridge, northwest Arabian Sea, indicate that an eolian transport mechanism predominated over the past one million years. Spectral comparison of the lithogenic grain size and flux records, in addition to comparisons with independent eolian records, indicate that the grain size record can be used as a paleoclimatic indicator of summer monsoon wind strength and the flux record as an indicator of aridity in the dust source-areas (primarily the Somali and Arabian Peninsulas).;The flux record is spectrally coherent and in phase the marine oxygen isotope record over all of the Earth's primary orbital frequencies (eccentricity, obliquity, and precession). This indicates that the timing of increases and decreases in regional aridity can be explained by the interplay between orbitally-induced insolation changes and the time constant of terrestrial ice sheets.;Spectral analyses of the grain size record indicates that the strength and timing of the paleomonsoon are forced externally by changes in insolation associated with the Earth's orbital precession and internally by the availability of latent heat collected over the Indian Ocean and released over the Asian Plateau. In contrast, sensitivity tests indicate that global climate model (GCM) paleomonsoon winds respond primarily to glacial boundary conditions and secondarily to insolation changes. Such discrepancies are clearly evident in comparison of results from GCM paleomonsoon simulations with the grain size record of monsoon wind strength and with faunal estimates of wind-induced upwelling in the Arabian Sea. These findings suggest the need for sensitivity experiments examining the role of latent heat exchange in current GCM's and for continued evaluation of methods for the model parameterization of energy exchanges across the ocean-atmosphere boundary.